CDC and WHO offer conflicting advice on masks. An expert tells us why.

The World Health Organization's guidance about when to wear a face mask may seem confusing to Americans, who have been advised by the Centers for Disease Control and Prevention to wear cloth face masks in public to help slow the spread of COVID-19.

"If you are healthy, you only need to wear a mask if you are taking care of a person with COVID-19," the WHO guidelines read.

Both organizations are considered to be reliable, authoritative sources of public health information. So why are they offering conflicting guidance on wearing masks during the pandemic?

The answer may come down to practicality, according to Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases.

At this point in the United States' outbreak, nearly everyone can find a mask or make one, Schaffner explained, which may not be true in every country around the world, especially countries with fewer resources than the U.S.

Advising universal mask wearing in a place where it's impossible to adhere to that guidance could hurt the WHO's reputation in those countries, he explained.

Another possible risk in places where masks aren't universally available is the potential for health care workers to be unable to get them, leaving them unprotected while caring for sick patients. Earlier in the U.S. outbreak, when masks were scarcer, Surgeon General Jerome Adams told everyday Americans to stop buying masks for this very reason.

"A lot of public heath is how can we take the theory and the science and bring it down the the average person," Schaffner said. "Public health has to be practical. Otherwise it doesn't work."

Editor's note: This story has been updated to reflect when the WHO's guidance was issued.

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